FLOW EQUATIONS AND BRS INVARIANCE FOR YANG-MILLS THEORIES

Flow equations describe the evolution of the effective action GAMMA(k) in the process of varying an infrared cutoff k. The presence of the infrared cutoff explicitly breaks gauge and hence BRS invariance. We derive modified Slavnov-Taylor identities, which are valid for nonvanishing k. They guarantee the BRS invariance of GAMMA(k) for k --> 0, and hence allow the study of non-abelian gauge theories by integrating the flow equations. Within a perturbative expansion of GAMMA(k), we derive an equation for a k dependent mass term for the gauge fields implied by the modified Slavnov-Taylor identities.